1. Field of the Invention
The present invention relates to a drying system having continuously connected close spiral conveyers, and more particularly to a drying system in which a plurality of substantially close spiral conveyers are connected end-to-end while they zigzag their way from top to bottom and are separately surrounded by a steam chamber so that some material passing the spiral conveyers is indirectly heated by the steam in the steam chambers and is evenly and thoroughly dried in the close spiral conveyers.
2. Description of the Prior Art
FIG. 1 illustrates a conventional tunnel drying system 1 which mainly includes an arcuated housing 11 provided at its surface with a plurality of through holes 12 and defining a passage 13 therethrough for a car 14 carrying material 15 to be dried to pass the housing 11 through the passage 13. A heater 16 is disposed outside the housing 11 such that the material 15 passing the housing 11 is directly heated by the heater 16. With this arrangements, the material 15 to be dried must be loaded on the car 14 in advance and then the car 14 is permitted to pass through the housing 11, permitting the material 15 to be heated by the heater 16 an become dried.
In such a conventional tunnel drying system 1, the material 15 is dried by means of direct heating. Since the material 15 is generally piled on the car 14 for heating, a portion of the material 15 exposed to the air or near an outer side of the pile is heated while the other portion thereof is not sufficiently heated. Moreover, since the material 15 is subjected to direct heating, it is difficult to precisely control the extend to which the material 15 is heated. It is possible the material 15 is either overheated or not sufficiently heated.
Therefore, the inventor has developed the present invention to eliminate the disadvantages existing in the conventional tunnel drying systems.